i965/vec4: Use nir_intrinsic_base in the load_uniform implementation
i965/vec4: Use nir_intrinsic_base in the load_uniform implementation

We shouldn't be reading the const_index directly

Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94998
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=95001

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler